There are various radio telecommunications networks co-existing and competing with varying services being offered and technologies being used. For mobile radio telecommunications, save perhaps satellite communications, it is typical that a moving mobile station makes handovers on its travel. In the handover, the mobile stations are switched to different base stations so that they can remain connected during the travel.
In GSM and W-CDMA, circuit switched and packet switched radio access are available to mobile terminals or mobile stations more generally. In the circuit switched access that is mostly used for speech communications, the call communication travels over radio interface between a mobile station and a serving Base Transceiver Station, over an Iub or Abis interface between the serving base station and network controller (named as Base Station Controller BSC or Radio Network Controller RNC in GSM and W-CDMA, respectively) and over an Iu interface between the controller and a Core Network (CN). In packet switched communications, the CN communicates with the RNC (or BSC) with a Serving Gateway Support Node (SGSN).
Normally, one controller controls a number of different base stations, but in particular new technologies such as HSPA (High Speed Packet Access) a singular base stations are managed by dedicated controllers. That a base station or generally access point connects directly to an SGSN or a server interconnecting to the Internet can be referred to a flat radio architecture. In high-speed packet data transfer a flat radio node-B (base transceiver station) provides some advantages such as faster retransmissions. Flat radio node-B refers to a node-B that is adapted to directly communicate with a packet data network (e.g. Internet) entity. HSPA is known, for example, from US 2006/0018294A1 filed on 29 Jun. 2005, assigned to Nokia Corporation and hereby incorporated by reference. Generally, HSPA or also so-called I-HSPA (Internet High Speed Packet Access) is a pre-step towards 3GGP Long Term Evolution (SAE/LTE/release 8). I-HSPA uses LTE architecture with a release 5 or 6 radio interface to ensure a broad user base. It is assumed that I-HSPA is packet only solution and when CS services are needed BTS handovers UE to CS capable BTS.
I-HSPA can be used with a standard Rel5 SGSN, but it is assumed that system performs better if at least the SGSN is One Tunnel capable (1T was actually Nokia proprietary feature that is now standardized in 3GPP). Furthermore I-HSPA may be optimized further over the one tunnel solution. Mobile Broadband: The Global Evolution of UMTS/HSPA 3GPP Release 7 and Beyond (www.3gamericas.org/English/pdfs/wp_UMTS_Rel7_Beyond_FINAL.pdf) describes in chapter 4.3 the one tunnel or direct tunnel using which more scalable UMTS system architecture can be achieved by direct tunneling of user plane data between the RNC and the GGSN. In the one tunnel approach, the transport and control functionality of the SGSN are separated, resulting in a new distribution of functionality with the GGSN. The new SGSN controller (cSGSN) is performing all control functions of an SGSN while the enhanced GGSN (xGGSN) is responsible for SGSN and GGSN transport functionality for the majority of traffic.
In the I-HSPA or in flat radio in general, the mobility management in the network is challenging as every time when a mobile station is handed over from one BTS to another, the RNC also changes and related mobility management operations are needed. Further, paging and location updates add signaling the more the fewer base stations are associated with individual RNCs. This further adds processing load to the serving gateway support node. Smaller routing areas result in less signaling on paging but increased handovers from one node-B to another.
In HSPA, if a node B is enabled to operate as a radio network controller (RNC), the RNC is seen by associated SGSN in a same way as a normal RNC that controls a multitude of BTS's. Hence, to ensure continuous operation, each SGSN in an HSPA enabled telecommunications network has to be dimensioned to have sufficient capacity to survive excessive mobility management that follows if all the connected RNCs are actually HSPA node Bs. Conversely, some of the SGSNs are over-dimensioned with regard to the actual need.